Pouring sugar in a gas tank will not ruin a motor like most of you think. But it will cause problems. Sugar does not dissolve in Gas. Therefore it stays a solid and will most likely be blocked by the fuel pump sock or the fuel filter. In the unlikely chance that any of the sugar particles would get passed either of the filters it may partially clog an injector. But on more modern vehicles the fuel system runs at high pressures and would most likely would just clear itself.
Also dont waste your money on octane booster. That will only make the car run sluggish.
A measure of a gasoline's resistance to exploding too early in the engine cycle, which causes knocking. The higher the rating, the lower the chance of premature ignition.
Basically the highr the rating the harder it is to ignite.
Cheaper idea fill five gallon gas can with four gallons of water 1 gallon of gas. The gas is lighter so it will sit on top so when they open the can they will still get the smell. And will give the same effect if not worse than the octane booster.
I cant think of any fuel mixtures that would truly damage an engine. But you could leave a quart of oil filled with sand and oil mixture and hope they take that and use it in there next oil change.